Ferrugem asiática e produtividade da soja sob doses de potássio e fungicida, na safra 2007/08

Abstract

Potassium has a major impact on plant diseases. Thus, the objective of this research was to evaluate the effect of potassium fertilization with and without fungicide sprays on asian soybean rust incidence and severity, in Dourados - MS, Brazil, in the 2007/08 cropseason. The experiment was conducted in Oxisol (Typic Haplustox), cultivated on no-tillage system on corn mulching. The experimental design was a randomized complete block with six replications, and treatments arranged in split-plots (plots - five K2O rates (0; 40; 80; 120 and 160 kg ha-1) using as fertilizer the potassium chloride (KCl) and subplots (presence and absence of fungicide sprays with azoxystrobin+ciproconazole). The incidence and severity of asian soybean rust, yield and 100 grains weight were analyzed. Fungicide application was essential for asian soybean rust control resulting in yield increase as well as weight of 100 grains. Without chemical protection yield was reduced in 22% (574.1 kg ha-1), and the weight of 100 grains decreased 18.6%. The rate of 80 kg ha-1 K2O associated with fungicide application was promising to reduce the deleterious effects of asian soybean rust considering the incidence in the middle portion and the upper third of the plants and severity in the upper third of the soybean plants.